Anamorphic Lens Corrects F Number Variation in Reflective Scanning
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Solution Overview
Problem
Conventional reflective scanning optical systems experience F number variation and changes in spot diameter and scan line interval due to the variation in the convergence angle of the laser beam, which is challenging to correct, especially in multibeam scanning systems, and requires high assembly accuracy or complex curved mirror surfaces, increasing manufacturing costs.
Innovation Solution
The implementation of an imaging optical system with a curved mirror and an anamorphic lens having a rotationally asymmetric surface, where the slope and curvature of the lens surface change along the main scanning direction to maintain constant magnification and F number, reducing the impact of manufacturing errors and simplifying the mirror surface configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a curved mirror with complex surface shape is used to correct F number variation, then the spot diameter can be kept constant, but the manufacturing cost increases
Solution Approach 1:
The patent applies asymmetry by using an anamorphic lens with different curvature radii in the main scanning direction (Ry) and auxiliary scanning direction (Rz). This asymmetric lens design corrects F number variation and maintains constant spot diameter without requiring complex curved mirror surfaces, thereby reducing manufacturing cost while achieving the desired optical performance.
Solution Approach 2:
The patent replaces the complex curved mirror surface (mechanical/optical surface shaping) with an anamorphic lens that has different refractive powers in different directions. This substitution achieves the same correction effect for F number variation but with simpler manufacturing processes and lower costs associated with lens fabrication compared to precision mirror surfacing.
2Manufacturing precision
If high assembly accuracy is required to cancel F number variation, then the spot diameter change can be suppressed, but the assembly process becomes extremely difficult
Solution Approach 1:
The patent changes the optical parameters by introducing an anamorphic lens with specific refractive powers in different directions (different curvature radii Ry and Rz). This parameter change in the lens design inherently compensates for F number variation and magnification changes, making the system less sensitive to assembly errors and simplifying the assembly process while maintaining spot diameter uniformity.
3Speed
If a conventional imaging optical system with fθ lens group is used, then scan speed correction is achieved, but chromatic aberration increases and system size increases
Solution Approach 1:
The patent replaces the conventional fθ lens group (refractive optical system) with a reflective scanning optical system using a curved mirror and anamorphic lens. This substitution eliminates chromatic aberration inherent in lens-based systems while maintaining scan speed correction functionality, and the compact arrangement reduces overall system size.
Solution Approach 2:
The patent extracts the chromatic aberration problem from the system by removing the fθ lens group and replacing it with a reflective system. The anamorphic lens is specifically designed to provide only the necessary scan speed correction and F number variation correction without introducing chromatic aberration, thus extracting the harmful chromatic effect while retaining useful functions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively suppresses F number variation, maintains constant beam spot diameter, and equalizes scan line intervals, even in multibeam systems, while reducing manufacturing complexity and costs by using simpler lens surfaces instead of complex mirror surfaces.
Implementation Method 1
an elongate lens having an anamorphic lens surface configuration on which slope and curvature of a line of intersection of a lens surface and a plane parallel to an auxiliary scanning cross section change as the plane gets further from the auxiliary scanning cross section in the main scanning direction
Implementation Method 2
a curved mirror for reflecting the dynamically deflected laser beam
Data Source
AI summary
In a reflective scanning optical system employing an imaging optical system having a curved mirror with a rotationally symmetrical reflecting surface configuration, the change in magnification of the imaging optical system in the auxiliary scanning direction is reduced and thereby the beam spot diameter on the scan target surface is equalized, as well as equalizing the scan line interval on the scan target surface when the system is applied to a multibeam scanning optical system. The imaging optical system of the reflective scanning optical system includes a curved mirror with a rotationally symmetrical reflecting surface and a lens having an anamorphic lens surface configuration on its one side. In the anamorphic lens surface configuration, slope and curvature of the line of intersection of the lens surface and a plane parallel to the auxiliary scanning cross section change independently of each other as the position in the main scanning direction changes.